1. Field of the Invention
This invention generally relates to telephone networks, and, more particularly, to a system and method for measuring a round trip time delay of voice packets in a telephone network.
2. Description of the Related Art
Typically, telephone systems for private organizations are set up as private branch exchanges (PBX). PBX sites allow for a plurality of telephones to share a set of lines for communicating between the telephones at the site and external telephones. Each telephone is connected to a cabinet. A cabinet is a physical box holding the wires, hardware, and software needed to forward information to and from the telephones.
Most cabinets at PBX sites are connected through physical means, such as fiber optic, connections. This requires many physical connectors be in place. It is preferable to use a local area network (LAN) to connect cabinets at a PBX site because typically all the users associated with that PBX already have a LAN connecting them. One problem with using a LAN is the delays created can distort the voices.
Software measurements of the delay are not accurate because they use an upper layer software protocol, and the coarse granularity software-based timers provides measurements that are sometimes an order of magnitude greater than the actual delays introduced by the network.
It would be desirable to measure delays caused by the LAN so that a customer may be notified of delay problems before the telephone system deteriorates and voices are transmitted distorted. It would also be desirable to know the delay so that if voices are distorted the customer knows that it is the LAN causing the distortion.
Systems and methods consistent with the present invention include structure and steps for measuring a round trip delay of voice packets in a telephone network.
A system for use in a telephone network consistent with the present invention comprises structure for setting a transmit bit in an outgoing packet and for starting a timer at the setting of the transmit bit and structure for reading a receive bit in a received packet and for stopping the timer in response to the reading of a set receive bit in the received packet.
A system and method consistent with the present invention include structure and steps for constructing an outgoing first voice packet, setting a transmit bit in the first voice packet, starting a timer upon the setting of the transmit bit. In one embodiment the systems and methods consistent with the present invention further include structure and steps for receiving a second voice packet, checking the second voice packet to determine if a receive bit is set, and stopping the timer if the receive bit is set.
Another system consistent with the present invention includes a timer, a transmitting protocol state machine and a receiving protocol state machine. The transmitting protocol state machine comprising structure for assembling a first voice packet from voice samples, the first voice packet including a receive bit and a transmit bit, structure for setting the transmit bit in the first voice packet, structure for starting the timer upon the setting of the transmit bit, and structure for transmitting the first voice packet. The receiving protocol state machine comprising structure for receiving a second voice packet, the second voice packet including a receive bit and a transmit bit, structure for reading the receive bit and the transmit bit in the second voice packet, structure for setting the receive bit on the first voice packet assembled by the transmitting protocol state machine in response to reading a set transmit bit in the second voice packet, and structure for stopping the timer in response to reading a set receive bit.
Another system consistent with the present invention includes a cabinet for use in a telephone network transmitting packets, the cabinet comprising a link for communicating with external devices and structure for connecting to a set of telephones. The link includes structure for setting a transmit bit in an outgoing packet and for starting a timer at the setting of the transmit bit and structure for reading a receive bit in a received packet and for stopping the timer in response to the reading of a set receive bit in the received packet.
Both the foregoing general description and the following detailed description explain examples of the invention and do not, by themselves, restrict the scope of the appended claims.